Advice - advise
There are two closely related words that can be confused.
- The verb is 'to advise'. (This sounds as though it were written with the letter 'z' - technically, a voiced consonant.) The spelling with '-ise' "is compulsory" (Burchfield's Fowler), and advise is one of Hart's list of 30 common verbs which are properly spelled with -ise, as is misadvise. These spellings are connected to the fact that they entered English from the French avis, and not directly from the ancestral Latin advīsāre.
- The related noun is advice. (This sounds as though it were written with the letter 's' - technically an unvoiced consonant.)
Non-native speakers sometimes use the noun advice as a countable noun. This is a mistake. Advice is non-count. If you need a singular form, use the countable expression "a piece of advice" or "a bit of advice", or re-phrase your sentence with the verb: "He hoped that she would advise him."